Schiff’s test

Solution in aqueous NaaCOa reduces silver nitrate (Schiff s test). 

Schiff s test. Dissolve about o i g. of uric acid in NsjCOj solution and pour some of this solution on to a filter-paper which has been moistened with AgNO solution a black stain of metallic silver results. 

A common method for distinguishing between aldehydes and ketones is Schiff s test. Aldehydes give positive tests, whereas ketones do not. 

Detection of Uric Acid.—(i.) Bedudim Tests.— Urio acid in alkaline solution can reduce silver salts (Schiff s test), copper salts, phosphomolybdates and phosphotungstates. The last of these reactions is the basis of Folin s method for detection and estimation of the acid. 

Gives some of the tests for acetaldehyde, but more feebly e.g., it restores the colour to SchifF s reagent, gives a yellow resin with NaOH, and responds to the nitroprusside test. With ammoniacal AgN03, it gives a silver minor only after 2 -3 minutes warming. It does not give the iodoform reaction. 

An alternative procedure for the above test is as follows. Mix 2-3 ml. of 2 per cent, aqueous paraperiodic acid solution with 1 drop of dilute sulphuric acid (ca. 2 5N) and add 20-30 mg. of the compound. Shake the mixture for 5 minutes, and then pass sulphur dioxide through the solution until it acquires a pale yellow colour (to remove the excess of periodic acid and also iodic acid formed in the reaction). Add 1-2 ml. of Schiff s reagent (Section 111,70) the production of a violet colour constitutes a positive test. 

Schiff s reagent analy chem An aqueous solution of rosaniline and sulfurous add used in the Schiff test. shifs re,a-(3nt ... 

Detection of Aldehydes.—100 c.c. of the vinegar are neutralised exactly with caustic soda and distilled, the first 10 c c. of distillate being tested for aldehyde by means of Schiff s reagent p. 244). 

Schiff s reaction. 10 c.c. of the alcohol (50%) and 4 c.c. of Schiff s reagent (see below r Determination) are shaken together in a test-tube and allowed to stand. The presence of aldehydes is shown by the appearance, either immediately or after some time, of a more or less intense red coloration, which should be observed after about 20 minutes. If no colour appears after this time, the liquid is free from aldehydes. 

Procedure. 10 c.c. of the spirits, brought to 50% strength, are placed in one test-tube and 10 c.c. of the standard solution in another, 4 c.c. of Schiff s reagent being added in each case and the tubes then dosed, shaken and left for 20 minutes. If the two liquids then have about equally intense colorations, they are compared in the colorimeter. Otherwise the test is repeated, a less quantity being taken of the alcohol giving the deeper coloration and this made up to 10 c.c. with pure 50% alcohol this is necessary because the intensities of the coloration are not proportional to the aldehyde-content, except when the differences are small. When sensibly similar colorations are obtained, the liquids are compared in the Duboscq colorimeter. 

The presence of aldehydes is tested for by treating 3-4 c.c. of the distilled spirit with 3-4 c.c. of Schiff s reagent. If no coloration or only a faint pink appears, the presence of aldehydes is excluded. 

Buchanan, Dekker and Long used periodate oxidation, followed either by Schiff s reagent (for cis-diols) or potassium iodide (for triols). The test is general for non-reducing carbohydrates having the necessary configuration of hydroxyls. Lead tetraacetate oxidation requires no further reagent to reveal the spot.66... 

The presence of hexosamine in the hydrolyzate of a mucopolysaccharide may well be indicated on the basis of the above colorimetric tests and the amount present estimated. The identity of the amino sugar cannot thereby be established, since the colorimetric methods cannot differentiate between glucosamine, chondrosamine or any other 2-amino sugar. The ideal means for the identification of a hexosamine is the isolation of a well characterized crystalline derivative. Numerous compounds for this purpose or of potential application have been recorded in the literature but only in the case of the Schiff s bases have satisfactory results been obtained. 

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